Edge-of-dock leveler and method of making

ABSTRACT

An edge-of-dock leveler incorporating an inflatable lift bag. The leveler includes a frame mounted on the front face of the dock and the rear edge of a deck plate is hinged to the frame, while a lip is hinged to the forward edge of the deck plate. In the storage position, the deck plate is generally horizontal while the lip hangs downwardly in a pendant position. The frame includes a fixed pressure member and a movable pressure member is hinged to an edge of the fixed pressure member. A link interconnects the movable pressure member with the deck plate. An inflatable, flexible bag is located between the pressure members and by inflating the bag, the deck plate is pivoted from the horizontal position to the substantially vertical position. By deflating the bag, the deck plate will descend by gravity and the forward edge of the lip will move in a generally curved path into engagement with the bed of a truck parked in front of the loading dock.

This is a continuation of application Ser. No. 08/131,990, filed Oct. 4,1993, entitled "EDGE-OF-DOCK LEVELER", now U. S. Pat. No. 5,450,643.

BACKGROUND OF THE INVENTION

Dock levelers are mounted on a loading dock and are adapted to span thegap between the loading dock and the bed of a carrier or truck parked infront of the dock so that material handling equipment, such as a lifttruck, can move conveniently between the dock and the truck bed.

One common form of dock leveler is mounted in a pit or recess formed inthe dock surface and includes a ramp or deck plate which is stored in agenerally horizontal position flush with the upper surface of the dockand is movable to an upwardly inclined position. A lip is hinged to theforward edge of the ramp and can be pivoted between a downwardly hangingpendant position, and an extended position where the lip forms anextension to the ramp.

Another form of dock leveler is a type known as an edge-of-dock levelerwhich is mounted to the front surface of the dock and thus does notrequire a preformed pit in the dock and can be utilized with existingdocks. The conventional edge-of dock leveler includes a deck plate whichis hinged to the frame of the leveler and a lip is pivotally connectedto the forward edge of the deck plate. In the storage position, the deckplate is generally horizontal and the lip hangs downwardly in thependant position. To move the leveler to an operating position, the deckplate is pivoted upwardly to a generally vertical position thuselevating the lip to a position above dock level, and the deck plate andlip are then moved forwardly to enable the lip to engage the bed of thetruck.

In the past, the typical edge-of-dock leveler has been operatedmanually. For example, an operator, standing on the dock and using along hook-like implement, engages the deck plate and pivots the deckplate upwardly to the vertical position. The lip is then engaged by theimplement and pivoted to the extended vertical position, and the leveleris then lowered to bring the extended lip into engagement with the truckbed. Because of the weight of the deck plate and the lip, it is verydifficult to manually pivot the deck plate and the lip upwardly to thevertical position,

To facilitate the lifting of the deck plate and the lip to the verticalposition, it has been proposed to incorporate a counterbalancingmechanism. Not only is a counterbalancing mechanism expensive, adding tothe cost of the unit, but the counterbalancing mechanism exerts anupward force on the deck plate and may tend to prevent firm contactbetween the lip and the truck bed, particularly when a fork lift truck,or other load, jars the deck plate, as the fork lift truck moves acrossthe deck plate.

It has also been proposed to utilize a hydraulic system to move the deckplate and lip of the edge of dock leveler to the upper or verticalposition. In a typical hydraulic system, a hydraulic cylinder unit isinterconnected between the frame of the leveler and the deck plate.However, the use of a hydraulic system substantially increases theoverall cost of the leveler.

SUMMARY OF THE INVENTION

The invention is directed to an edge-of-dock leveler incorporating aninflatable bag to move the deck plate from the horizontal to thevertical position. The leveler includes a frame which is attached to thefront face of the loading dock, and the rear edge of a deck plate ispivoted to the frame. The deck plate is movable from a generallyhorizontal storage position, to an upper generally vertical position.Hinged to the forward edge of the deck plate is a lip and in the storageposition, with the deck plate horizontal, the lip hangs downwardly in apendant position.

In accordance with the invention, the frame includes a fixed pressuremember which preferably extends substantially the entire side-to-sidewidth of the leveler, and a movable pressure member is hinged to an edgeof the fixed pressure member. A linkage pivotally interconnects themovable pressure member with the deck plate.

Located between the pressure members is a flexible inflatable bag and byinflating the bag through use of low pressure air or other gas, themovable pressure member will be pivoted upwardly thereby pivoting thedeck plate from the horizontal storage position to a substantiallyvertical position.

The deck plate and lip are held in the elevated vertical position by alocking bar which engages an abutment on the leveler frame. In thisupper position, the lip is located at an acute angle with respect to thedeck plate and the lower edge of the lip is located above dock level.

By discontinuing operation of the fan or blower, the bag will deflateand the deck plate will descend by gravity toward the horizontalposition. The locking bar enables the outer edge of the lip to move in agenerally curved path, thus ensuring that the lip will clear the bed ofthe carrier and move downwardly into engagement with the carrier bed.

With the construction of the invention, the deck plate and lip can bepivoted from the storage position to the upper vertical position withoutmanual effort through inflation of the flexible bag.

The invention provides an inexpensive edge-of-dock leveler which has allthe advantages of a hydraulic operated edge-of-dock leveler, but whichhas a substantially reduced cost.

In the operative position, with the lip engaged with the bed of thetruck or carrier, the entire weight of the deck plate and lip is on thetruck bed, so that there is no tendency for the leveler to jack-knife asmaterial handling equipment travels over the leveler from the loadingdock to the truck bed.

As a further advantage, when the bag is deflated, the air from the bagpasses back through the fan or blower, thus providing a controlleddescent for the deck plate and lip to prevent the lip from banging downonto the carrier bed.

Other objects and advantages will appear in the course of the followingdescription.

DESCRIPTION OF THE DRAWINGS

The drawings illustrate the best mode presently contemplated of carryingout the invention.

In the drawings:

FIG. 1 is a perspective view of the edge-of-dock leveler of theinvention with the deck plate in the horizontal cross-traffic position;

FIG. 2 is a vertical section of the leveler with the deck plate shown inthe horizontal cross traffic position;

FIG. 3 is a view similar to FIG. 2 showing the deck plate and lip in anupper elevated position;

FIG. 4 is a front elevation of the leveler, with the deck plate and lipin the elevated position;

FIG. 5 is a fragmentary enlarged vertical section showing the attachmentof the bag tether to the fixed pressure plate;

FIG. 6 is a vertical section of the leveler showing a modified form ofthe invention and illustrating the deck plate in the horizontal crosstraffic position; and

FIG. 7 is a view similar to FIG. 6 showing the plate and lip in anelevated position.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

The drawings illustrate an edge-of-dock leveler 1 mounted on the frontface 2 of a loading dock 3. The leveler 1 is adapted to span the gapbetween the loading dock and the bed 4 of a truck or other carrier,which is parked in front of the loading dock.

Leveler 1 includes a frame or supporting structure 5 composed of avertical plate 6 that is mounted to the front face 2 of dock 3, andbox-like frame members 7 are connected to opposite ends of plate 6. Inaddition, a horizontal plate 8 is coextensive with plate 6 and isconnected to the lower ends of frame members 7.

Bumpers 9 are mounted on the outer extremities of frame members 7 andare positioned to be engaged by the rear end of the truck 4, as thetruck backs toward the loading dock, to prevent damage to the leveler.Each bumper 9 includes a pair of spaced vertical angles 10, which aremounted on either side of a series of resilient strips 11.

Leveler 1 includes a deck plate 12 and a lip 13. To pivot the rear edgeof the deck plate 12 to frame 5, hinge tubes 14 and 15 are secured tothe deck plate 12 and to plate 6. Hinge tubes 14 and 15 are in staggeredaligned relation and are connected by a suitable hinge pin, thusenabling the deck plate 12 to be pivoted relative to the frame 5.

To pivotally connect lip 13 to the forward edge of the deck plate 12, aseries of hinge tubes 16 are secured to the deck plate and are mountedin staggered alignment with hinge tubes 17 which are secured to strip 19that, in turn, is welded to the rear end of lip 13. Hinge pin 20interconnects the hinge tubes 16 and 17 to permit the lip to pivotrelative to the deck plate. As the lip 13 pivots upwardly relative tothe deck plate 12, the rear edge of the lip will engage the forward edgeof the deck plate to limit the pivotal movement of the lip, so that thelip will not move beyond a position which is generally flush with thedeck plate. Deck plate 12 is maintained in the generally horizontalcross-traffic position by engagement with a series of lugs 21 which arewelded to plate 6 and project forwardly from the plate, as seen in FIG.2.

As best illustrated in FIG. 2, an upper movable pressure plate or member22 is pivoted to the forward edge of the horizontal plate or fixedpressure member 8. To provide this pivotal connection, the plate 8 andplate 22 are provided with aligned hinge pins 23 and 24 which areinterconnected by hinge pin 25. This connection enables the pressuremember 22 to pivot upwardly relative to the lower fixed pressure member8. Located between pressure members 8 and 22 is a flexible bag 26,preferably formed of plastic material. In practice, the bag may beformed of nylon fabric impregnated with a thermosetting resin, such aspolyethylene.

To inflate the bag, a fan or blower 27 is mounted on the lower end ofplate 6, and the outlet of the fan 27 is connected via a conduit 28 to afitting 29 in bag 26. Fan 27 is adapted to supply low pressure air,generally in the range of 0.5 to 5.0 psig to the bag to thereby inflatethe bag.

Connecting the upper pressure member 22 with the deck plate 12 is a pairof links 30. As shown in FIG. 2 and 3, the low end of each link 30 ispivotally connected to a pair of lugs 31 on plate 22, while the oppositeend of each link is pivoted to lug 32 on the underside of deck plate 12.The links 30 increase the magnitude of pivotal movement of deck plate12, thus enabling a smaller volume bag 26 to be used.

To prevent bag 26 from squeezing rearwardly as it is inflated, the bagis secured or tethered to plate 8. In this regard, a tether strip 33 isattached to bag 26, and extends forwardly away from dock 3. Tether strip33 preferably extends the full width of bag 26 and is attached to plate8 through a retaining strip 34 and a series of spaced bolts 35. Thetether 33 will prevent bag 26 from squeezing rearwardly as the bag isinflated to pivot deck plate 12 to the vertical position.

FIG. 2 shows the dock leveler in the storage position, in which the deckplate 12 is supported on supports or stops 21. In the storage position,deck plate 12 is generally horizontal and lip 13 is pendant asillustrated in FIG. 2.

To move the dock leveler to the operative position, fan 27 is operatedto thereby supply air through line 28 to bag 26 to inflate the bag.Inflation of bag 26 pivots the upper pressure plate 22 upwardly and thuspivots the deck plate 12 upwardly, as illustrated in FIG. 3. In thisposition, the deck plate 12 is in a substantially vertical position, andis held in this position by a locking bar 37. As best shown in FIG. 3,the upper end of the lock bar is pivotally connected to a pair of lugs38 on the underside of lip 13. When the deck plate is pivoted upwardlythrough inflation of bag 26, the rear edge of lugs 38 will engage thedeck plate to hold the lip 13 outwardly at an acute angle relative tothe deck plate, and a notch 39 on the lower end of locking bar 37 willengage a horizontal rod 40, which is supported through lugs 21 thatproject outwardly from plate 6 of frame 5. In the position shown in FIG.3, the locking bar 37 is in an over-center position at a slight angle tothe vertical.

Operation of fan 27 is then discontinued and the deck plate 12 and lip13 will then pivot downwardly by gravity. As the deck plate 12 pivotsdownwardly, locking bar 37 will initially pivot to a centered orvertical position and then to an undercenter position, causing the pivotbetween the locking bar and the lugs 38 to move in an upward curvedpath. Due to the position of the pivots, the outer tip of lip 13 willinitially describes an upwardly curved path of travel which enables thelip to clear the bed of the truck 4, even though the truck bed may belocated above dock level. Subsequent downward pivotal movement of thedeck plate will cause the lip to engage the bed of the truck. Theconstruction of locking bar 37, along with the movement of the lip 13,in engaging the truck bed is similar to that described in U. S. Pat. No.3,685,077.

After the loading or unloading operation has been completed, the truckmerely pulls away from the dock, causing lip 13 to pivot downwardly tothe pendant position, and the deck plate will pivot downwardly until itengages the stops 21 to limit its descent and maintain the deck plate inthe generally horizontal storage position.

Through use of the inflatable bag 26, the deck plate 12 and lip 13 arepivoted upwardly without manual effort. The system thus has all theadvantages of a hydraulically operated system, but with substantiallyreduced cost.

As no counterbalancing system is utilized, the entire weight of the deckplate will rest on the truck bed and there is no tendency for the dockleveler to jack-knife as material handling equipment, such as a forklift truck, passes over the dock leveler in travel between the loadingdock and the truck bed.

On termination of operation of fan 27, the deck plate 12 will pivotdownwardly causing the air in bag 26 to be exhausted through the fan.This restricted exhaust of the air will provide a slow and controlleddescent of the deck plate to the operative position.

FIGS. 6 and 7 illustrate a modified form of the invention in which theupper pressure plate 22a is hinged to the rear edge of lower pressureplate 8, rather than being hinged to the front edge as in the embodimentof FIGS. 1-5. A pair of links 30a, corresponding to links 30 of thefirst embodiment, pivotally connect the forward edge of upper pressureplate 30a with the underside of deck plate 12. In the construction ofFIGS. 6 and 7, inflation of bag 26 through operation of fan 27 willpivot the deck plate 12 upwardly to a generally vertical position, asillustrated in FIG. 7. Except for the reversal of the pivotal connectionbetween the pressure members, the construction of FIGS. 6 and 7 is thesame as that of FIGS. 1-5.

I claim:
 1. A dock leveler for mounting on a loading dock, comprising:asupporting structure attachable to the loading dock; a deck plate havinga rear end pivotally connected to said supporting structure; aninflatable bag operatively positioned to pivot said deck plate uponinflation and deflation of said bag; inflating means for introducing agas under pressure into said bag to selectively inflate and deflate saidbag, thereby resulting in pivotal movement of said deck plate; and meansfor preventing displacement of said inflatable bag, wherein said meansfor preventing displacement comprises a tether interconnecting said bagwith said supporting structure.
 2. The dock leveler of claim 1, furthercomprising:a first pressure member interconnected with said supportingstructure; and a second pressure member mounted for movement relative tosaid first pressure member and operatively connected to said deck plate,wherein said inflatable bag is disposed between said first and secondpressure members.
 3. The dock leveler of claim 2, further comprising alinkage interconnecting said second pressure member and said deck plate.4. The dock leveler of claim 2, wherein said tether interconnects saidbag and said first pressure member.
 5. The dock leveler of claim 3,wherein said linkage includes a rigid link having one end pivotallyconnected to said second pressure member and the opposite end connectedto said deck plate.
 6. A method of making a dock leveler, comprising thesteps of:pivotally connecting a rear end of a deck plate to a supportingstructure; attaching a bag support to the supporting structure;positioning an inflatable bag on the supporting structure such that thedeck plate is pivoted upon inflation and deflation of the bag; andsecuring one portion of a tether to the inflatable bag and anotherportion of the tether to the bag support.
 7. A dock leveler,comprising:a supporting structure; a deck plate having a rear endpivotally connected to said supporting structure; a movable pressuremember positioned under said deck plate; a linkage memberinterconnecting said pressure member with said deckplate, said linkagemember being pivotally connected with said deck plate at a first pivotlocation and pivotally connected with said movable pressure member at asecond pivot location different than the first pivot location; and aninflatable bag operatively positioned to move said pressure member,thereby causing pivotal movement of said deck plate.
 8. The dock levelerof claim 7, wherein said dock leveler further includes a tetherextending from said inflatable bag toward said pivot location.